This invention relates to a process for simulation of the response of a detector of radiation emitted by radioactive objects and a process for inspection of nuclear fuel elements using this simulation.
It is particularly applicable to the inspection of nuclear fuel rods that contain stacks of pellets of this fuel, these pellets emitting xcex3 radiation.
It is known how to inspect a set of rods of this type to verify the homogeneity of pellets in a given category.
In order to do this, a preliminary calibration is made of the xcex3 radiation measurement system used for the inspection. For example, the detector for this system is described in documents FR-A-2437002, EP-A-0009450 and JP-A-1527161 that includes an annular scintillator that is preferably made of sodium iodide activated with thallium NaI(Tl).
This calibration also involves making specific rods and passing them in front of the detector, to obtain what are referred to in statistics as regression straight lines, and which in this case give the response of the detector to powder mixes used in the pellets depending on the content of their components (for example uranium and plutonium), for homogenous portions of rods or for isolated pellets in one category among a group of pellets of another category.
This requires a large number of measurements and an equally large number of calibration rods representative of these typical situations, but unusable in a reactor.
The purpose of this invention is to overcome the disadvantages mentioned above by proposing a process that can economically control nuclear fuel rods, or more generally nuclear fuel elements. In this process, the preliminary calibration of the measurement system is eliminated and is replaced by a simulation of the response of the measurement system detector, in other words the count made by this measurement system.
Specifically, the initial purpose of this invention is a process to simulate the response of a radiation detector detecting radiation emitted by radioactive objects, these objects containing radioelements or mixes of radioelements, this process being characterized in that:
radioactive emission spectra representative of radioelements or mixes of radioelements are memorized,
the detection characteristics of the detector are determined,
the operating characteristics of received radiation are determined,
radioelements or mixes of radioelements among hose for which spectra have been memorized are elected, and
the detection characteristics and operating characteristics are processed so as to individually reproduce radiation emitted for the chosen radioelements or mixes of radioelements, to obtain the simulated detector response.
Preferably, the detection characteristics comprise data representative of the thickness through which the radiation passes before it is detected.
Also preferably, operating characteristics also include the detector aperture angle, detected energy bands and electronic amplification characteristics of the detector.
According to a preferred embodiment of the process according to the invention, regression straight lines are also built up starting from the simulated response.
For example, the detector may be a xcex3 radiation detector and the invention is applicable particularly in the case in which the said objects are nuclear fuel elements.
The invention also relates to a process for the inspection of a set of nuclear fuel elements using the simulation process (applied to objects composed of these elements), inspection process in which:
the real composition of any of the elements of the assembly is analyzed,
the detector is calibrated with this element for which the real composition has been analyzed,
the simulated response is corrected using the response of the detector obtained during calibration, and
all elements are inspected.
For example, the elements may be nuclear fuel rods, these rods including stacks of pellets from this nuclear fuel.
For example, in this case the detector may comprise an annular scintillator, and for example a sodium iodide scintillator may be used.